Parasitic battery drain

Thread Tools

Ford
F150 XL striped model a/c only - 7700 series CNG
2002
84k
5.4L
Thanks in advance for reading and offering suggestions. I just bought this vehicle and can't figure out the problem. My vehicle has a parasitic battery drain. After the vehicle sits for anywhere from 1 to 3 days I need to jumpstart the vehicle. The battery is new. I used my multimeter to test for the drainage and amperage being drained. The drain value is 0.17 amps then after 45min the drain goes to 0 amps. I suppose after the 45 min duration the battery saver kicks in creating the 0 drain result. (Might the battery saver be bad and not working sometimes?) When I unplug fuse #15 which is 5 amps and controls The stop lamp switch, speed control, brake shift interlock, GEN module and RABS module the drain also shows 0 amp draw. I tried ruling out the break pedal switch and have unplugged the switch at the break pedal but the amp draw remained the same 0.17 amps. I don't know what the other items are that are on this circuit. Once again, thanks for your help!

If you disconnect one battery cable, will the battery then stay charged OK? That 170mA shouldn't be enough to run the battery down that quickly. Also, going to "zero" doesn't sound right, there is almost always a small current load in modern cars to keep memory alive on radios, power seats, etc. Got it? I'm kind of confused about your symptoms, they aren't making sense to me.

Oh, and I should ask... what is the charging voltage when the engine is at 1500 rpm?

If you disconnect one battery cable, will the battery then stay charged OK? That 170mA shouldn't be enough to run the battery down that quickly. Also, going to "zero" doesn't sound right, there is almost always a small current load in modern cars to keep memory alive on radios, power seats, etc. Got it? I'm kind of confused about your symptoms, they aren't making sense to me.

Oh, and I should ask... what is the charging voltage when the engine is at 1500 rpm?

Click to expand...

If I remove the negative cable from the battery it will start the truck fine when reconnected. I just tried that las week while on vacation. I understand that the radio might require a small voltage for its memory and even when the vehicle drops to 0 amps after the 45 minute interval the radio retains its station settings I've tried this test several times and like clock work it drops to 0 amps after 45 min. Other than the radio, the only other options are A/C and intermittent wipers and a 4 pin trailer connector which is properly working. While at 1500 rpms the battery is charging at 14.04 v. While the vehicle is not running the battery reading is 13.13 v. I did try removing the battery saver fuse #14 which is a 15 amp fuse while leaving in the 5 amp fuse which is #15 and that shows a draw of 0.004 amps. Could the alternator be causing the drain? I'm puzzled!

I just completed the diode test on the alternator. The diodes are bad. I'll be replacing the alternator over the weekend. Thanks for your help. You truly saved me a lot of time and effort and I greatly appreciate your help!

I just completed the diode test on the alternator. The diodes are bad. I'll be replacing the alternator over the weekend. Thanks for your help. You truly saved me a lot of time and effort and I greatly appreciate your help!

Old school test is to disconnect neg batt terminal and put test light between terminal and post. If alternator disconnect does not dim the light then start pulling fuses one at a time to see light dim. When it dims you found the circuit